Philip H. Jones, Onofrio M. Maragò & Giovanni Volpe
Fig. 8.12 — Action of lenses illustrated with ray diagrams
(a) A plano-convex (positive) lens focuses an incoming collimated beam. (b) A plano-concave (negative) lens makes an incoming collimated beam divergent. (c) A telescope expands a beam. Note that the curved side of each plano-convex lens is turned towards the side where the beam is collimated (parallel rays) to minimise spherical aberration.
Fig. 8.12 — Action of lenses illustrated with ray diagrams